Single-cam and dual-cam compound archery bows have a power cam mounted on one or both ends of the bow limbs to control the draw force on the bowstring and bending of the limbs as the bowstring is drawn. In single-cam bows, there is a power cam on the end of one bow limb and a wheel on the end of the other bow limb to facilitate let-out of the bowstring as the bow is drawn. In dual-cam bows, power cams are mounted on the ends of both bow limbs, with each cam including groove segments to control let-out of the bowstring.
As bow performance has improved, there can be a problem of the bowstring staying in its let-out groove after the bowstring has been released by a user. This problem can be aggravated if the bow user torques or twists the bow handle so that the plane of the bowstring grooves on the pulleys moves away from the plane of travel of the bowstring. The use of bowstring bumpers, which are attached to the bow handle and cushion the bowstring at the end of the power stroke, sometimes tends to help alleviate this problem, but does not eliminate it. In some cases, the presence and/or location of the bumper annoys the shooter. High-performance bows can have a bowstring derailing problem when the user uses his or her fingers, rather than a mechanical release, to draw and release the bowstring. A general object of the present disclosure is to provide a pulley for a compound archery bow, and a compound archery bow that includes such a pulley, that reduces or eliminates the problem of bowstring derailing.
In current bow designs, the depth of the bowstring groove on the pulley is constant and equal to or slightly less than the bowstring diameter. In accordance with one aspect of the present disclosure, the radial depth of the bowstring groove on the pulley is at least 10% greater than the diameter of the portion of the bowstring that lies in the groove. In accordance with another aspect of the disclosure, the radial depth of the bowstring groove is non-constant around the periphery of its pulley, preferably being greatest about midway through the portion of the power stroke that builds to peak force, and then decreasing in both directions at the nose of the pulley and rest of the pulley's circumference.